I have a Logitech USB headset.
I go to System > Preferences > Hardware > Sound. Under the Devices tab I select USB device for everything. I even set Device to "Logitech USB Headset." I click each Test button. It beeps through the headphones just fine, so I know it's capable of using my headset. However, when I do anything else that uses sound, it plays the sound through my laptop's crummy speakers instead. How do I convince this stubborn operating system to use my precious headset?
(Edit) Never mind, I got it to work. I went to System > Administration > Soundcard Detection. I fiddled things around and bingo!